CVE-2026-12856
Description
A flaw was found in the vscode-java extension, which provides Java language support for Visual Studio Code. The extension incorrectly trusts all Markdown content in JavaDoc hovers, allowing a malicious Java file to include hidden commands. If a user clicks a specially crafted link within a JavaDoc hover popup, an attacker can execute arbitrary VS Code commands, which can lead to full system compromise in trusted workspaces.
Statement
The Red Hat Product Security team has assessed the severity of this vulnerability as Important, given that it requires a user to open a malicious Java source file and interact with a hover popup. Successful exploitation allows an attacker to execute arbitrary commands within the context of the VS Code editor and potentially the underlying operating system. The vulnerability's root cause is the over-trusting of Markdown content returned by the Java language server, which fails to isolate extension-generated trusted links from attacker-controlled JavaDoc content.
Mitigation
To mitigate this issue, users should avoid opening or interacting with untrusted Java projects or files within Red Hat OpenShift Dev Spaces. Exercise caution and refrain from clicking on unfamiliar links presented in JavaDoc hover popups, particularly when working with code from unverified sources. Disabling the `vscode-java` extension when not actively engaged in Java development can further reduce exposure, though this will impact Java-related functionality.
Common Vulnerability Scoring System (CVSS) Score Details
Info alert:Important note
CVSS scores for open source components depend on vendor-specific factors (e.g. version or build chain). Therefore, Red Hat's score and impact rating can be different from NVD and other vendors. Red Hat remains the authoritative CVE Naming Authority (CNA) source for its products and services (see Red Hat classifications).
CVSS v3 Score Breakdown
| Red Hat | NVD | cve.org | |
|---|---|---|---|
| Base Score | 8.8 | N/A | 8.8 |
| Attack Vector | Network | N/A | Network |
| Attack Complexity | Low | N/A | Low |
| Privileges Required | None | N/A | None |
| User Interaction | Required | N/A | Required |
| Scope | Unchanged | N/A | Unchanged |
| Confidentiality | High | N/A | High |
| Integrity Impact | High | N/A | High |
| Availability Impact | High | N/A | High |
Vector
Red Hat: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H
cve.org: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H
Understanding the Weakness (CWE)
Confidentiality,Integrity,Availability,Other
Technical Impact: Execute Unauthorized Code or Commands; Alter Execution Logic; Read Application Data; Modify Application Data
An attacker could include arguments that allow unintended commands or code to be executed, allow sensitive data to be read or modified or could cause other unintended behavior.
Acknowledgements
Red Hat would like to thank byte256 for reporting this issue.
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